Recumbent Trike with trailer & two hub motors

[Rassy]

Just found this forum a few days ago and first want to say thanks for so many interesting and informative discussions. I gave up on pedal bikes when I built my retirement home up a 1/3 mile steep hill (approaches 20% and topped by a short driveway that hits 23% grade). But I missed the bikes and got tired of walking back up the hill or taking the car each time I wanted to go to the store, etc. So my fourth project is working pretty good for me. It is an EZ-3 USX pulled by a 20" BD36 on the front and pushed by two 20" BD36's mounted on a small trailer I made just to accomodate the motors and batteries. All three controllers are run from the same throttle and the three SLA 36V battery packs are hooked together in parallel so everything stays fairly well balanced (Some of the discussions I read indicate I may be courting some battery problems with this setup?) Anyway, I normally just leave the trike in 12th (out of 21) gear and with moderate pedaling maintain 11 to 14 MPH up the hill. Because the hill terminates in a blind corner with rough pavement I installed a toggle on the trike which (with 800W relays) breaks the connection between the controllers and motors and connects each motor to 400w worth of 12v headlight bulbs. This makes a very effective motor brake and I just have to feather the trike brakes a little on the steeper parts to keep from blowing the light bulbs with too much voltage. The motors create 12 volts at about 10MPH so I don't let it go over 11MPH while using the motor brake.

Thanks again for great discussions and if anyone has suggestions for battery management that I should consider I would appreciate it.

 

[xyster]

A big web-foot welcome from a fellow Oregonian! I appreciate there's steep hills in our neck of the woods.

Your machine sounds very interesting. Can we see some pics of it? Am I correct in understanding this a FWD trike also being pushed by a two-hubmotor'd trailer?

All three controllers are run from the same throttle and the three SLA 36V battery packs are hooked together in parallel so everything stays fairly well balanced (Some of the discussions I read indicate I may be courting some battery problems with this setup?)

I can't see any problems with that so long as the packs are of roughly equal capacity. If using SLA batteries of differing capacities, it's better to first wire the batteries in parallel, and then in series so that each battery is balanced rather than the sets of batteries being balanced:
---12V:12V:12V--12V:12V:12V--12V:12V:12V----

 

[Rassy]

XYSTER, thanks for your battery suggestion, I had not even considered it and could easily make the change. My trike is a long wheel base delta (one wheel in front, two in the back) model. I will post a picture when I figure out how (seems like I read you can't upload pictures directly from the PC)

Even though I'm not into speed as most of the members here are, The discussions on batteries (I can see going to lighter ones when the SLA's give out) and controlers (I can see going to 48 volts and maybe removing the front motor) apply equally to my ride. I would also like to figure out a practical way to allow me to use the motor braking at any speed.

 

[Rassy]

Picture of trike with trailer

 

[xyster]

Looks very spiffy!

I've thought about a trike. Are there trikes like this with rear dropouts that could secure hubmotors -- to make a 3WD trike without the trailer?

 

[Lessss]

You would need back wheels more like this for hub motors so that there are drop outs for the hub to be retained by and attach a torque arm.


Ah foo, just look at the trailer.

 

[Rassy]

I saw one someplace, it looked just like the picture Lessss just posted. It would probably require a DIY like Thaddeus is working on. The Tadpole design is more stable for high speed use, I think.

 

[Lessss]

http://www.lightfootcycles.com/trikes.htm

 

[Geebee]

The Light foot trikes also have the option of an electric assist running through a derailuer, electric one side human power the other.

 

[Lessss]

I like em they are just expensive though.

 

[Rassy]

The motor on the front of the trike has been removed, so now there are only two motors on the two wheel trailer. The motors are now being run at 48V, and two 48V motors perform slightly better than three 36V motors. However, they do get a little warmer. I made my decision knowing that I may have some component failures, but plan to upgrade as needed. It helps that I was able to eliminate about 25 pounds, and that I now don't have to worry about tearing up the front fork.

Instead of 9 12AH SLA in a 3S3P configuration there are 8 12AH SLA in a 4S2P configuration. The extra battery went in the recumbent's BOB trailer to make it 48V also.

 

[BiGH]

i think in this case you did the right thing - until you're running motors at or near their limits, don't add extra motors - it just adds weight. Your ride will be more efficient using that extra weight to support more batteries. Depending what your goals are with this ride - its better to just vary the motor to get what you want.

 

[Ypedal]

Warm is no problem, HOT can be, but if you can hold your hand on the motor without too much discomfort ( as in OUCH>... !@#$^ that hurt ) .. you are fine and good to go.

The controllers however, how warm/hot do they get with that setup ?

 

[BiGH]

after the ride it was still at ambient temp (motor and controller!)

further testing is required / DEMANDED on private roads of course

 

[Rassy]

Thanks Ypedal. There was no problem touching the motors. Riding around town and using the motors a lot doesn't hardly heat them up. But the steep hill to my house at full throttle for a few of minutes does. The controllers didn't seem to heat up much at all, and I could always mount them outside of the tote if necessary. Only time will tell. I currently have two spare motors and one spare controller left over from my projects, so can't get too excited about breaking things.

 

[Desertprep]

Putting a hub motor in each of the rear wheels of a delta bent is not advisable unless you can find some way to simulate the work of a differential. If both wheels are traveling at relatively high speeds - and, more importantly, at exactly the same speed and you enter into a rather tight turn you run the risk of flipping the bike or east least dealing with wheel hop. When you make a turn you need to find some way to slow down the wheel on the inner side of the turn.

A good low cost electronic differential will open many avenues for electric vehicles. Until that happens you will need to find some way to work with a mechanical differential.

 

[fechter]

I don't think so. If one motor tries to go faster than the other, it will just draw less current. The difference will not be enough to cause wheel hop or any other handling malfunction. Two motors will behave much like a differential.

Consider what happens if you lift the wheel off the ground. The motor will spin much faster than it does when it's loaded. Under normal riding conditons, the motor is running at somewhat less than it's no-load speed. The difference in speed caused by cornering will be well within the normal loading range of the motors.

You could have a problem if you had two geared motors that were geared very low, like wheelchair motors. Even then, they would allow for some 'slip' between them during cornering.

 

[Desertprep]

Are you assuming that you will mount the motors in series or will you use a controller that will control 2 motors?

 

[vanilla ice]

When you make a turn you need to find some way to slow down the wheel on the inner side of the turn.

Why would you want to slow down the inside wheel?

A normal car diff (or big moto trike) puts all the power into the inside SLIPPING wheel for safety. So when you unload the inside tire in a fast turn, it stops the power from reaching the ground and you can't accelerate any more.

 

[lazarus2405]

Are you assuming that you will mount the motors in series or will you use a controller that will control 2 motors?

When using two motors in one vehicle, we are talking about using one controller per motor, with the throttle wired to both in parallel. That way, each motor and controller is completely independent of the other motor and controller. They will receive the exact same throttle signal, and thus output the same PWM duty cycle.

A diff won't be a problem for the reasons fechter stated. Since the wheels are not mechanically connected, they can spin independently, and at different speeds.

I believe that to run two motors off one controller (that is, a controller only designed for one motor), the could not be in series, only in parallel. You'd have to only use one Hall effect sensor, start with the wheels in the exact same position, and hope that the differences that would come from bumps and steering would not be enough to upset the controller and its PWM cycle. I honestly don't think it's possible. Besides, running two off one controller would automatically halve the available current to each motor. If each motor is only receiving half the current, it's only putting half the power on the ground. Instead of using two controllers and two motors to get the power of two motors, you'd be using one controller and two motors to get the power of one motor. I can tell you that one of those options wastes a lot of weight.

If both wheels are traveling at relatively high speeds... and you enter into a rather tight turn you run the risk of flipping the bike...

This is true of all vehicles. Entering relatively tight turns at relatively high speeds is typically a bad idea. That's not a matter of the diff, it's a matter of the center of mass relative to the width between wheels and radial velocity,

 

[fechter]

The problem pengyou is describing would be true for a mechanically connected pair of wheels, but having two motors in parallel will work like a very nice limited-slip differential.

With brushed motors, you could put them in series and it would behave just like a normal differential. One wheel loses traction and the other one gets no torque.

 

[Desertprep]

Cool! I am just getting my feet wet in this electric world.

When I was in high school I was in marching band. Whenever we did a parade we always had to put the people with short legs in the inner part of each line because whenever we turned the person on the end had to either mark time (stand still) or take really big steps to keep the whole line in line. The same principle is true with a vehicle with a left and right wheel. When you turn one wheel has to go a greater distance than another so either one has to slow down or the other has to speed up. The principle is true whether the device has a gasoline engine or electric motor. With a gasoline engine the speed DIFFERENCE to the left and right side of the vehicle is created by a machine called a DIFFERENtial. I have ridden in some simple 3 wheel vehicles in China, used mainly for agricultural purposes and found that even at slow speeds, 8-10 mph, you can feel some slippage and hopping of the wheels in an even moderate turn.

Are you saying that there is something intrinsic to electric motors that will control this phenomenon without the need of additional hardware/software? About year ago I did some research online and found a post on a forum of a grad student who was doing research on how to create an electronic differential for motorized vehicles. Also, when I was reading a review for a completely electric car that had a huge motor in each wheel (I believe it was a Saab, but not sure) there was mention of a sophisticated algorithm that had been developed for the computer inside the car to adjust the speed of the wheels in each turn.

This are my reasons for bringing up the need for the differential. As I said, I am a newbie to the electric motor thing...just passing along what I have read/seen in other situations. I would like to learn more about this so please feel free to send along URL's.

I know that if you put a wheel on the front and back of a bike - in line - there is definitely no problem.

Also, in a call to a company that sold multi motor controllers, the customer service agent told me that the job of the controller is to keep the motors spinning at exactly the same speed. They can even accommodate for variances in motor ability as they get old so that they both will spin at the same speed.

 

[fechter]

Interesting

Electric motors can make a good differential. The controllers we use on bikes are not sophisticated enough to give exact speed control. As the load on the motor increases, it slows down. This happens when you go up a hill. It would be a problem if the controllers held precise speed as you describe.

In the differential situation, the inside wheel has to slow down as you corner. The torque it produces will increase as it slows down. I can see in an extreme situation, it may slow down enough to cause problems. This would only happen doing a U-turn or very sharp turn. Even then, the torque it can produce will be limited by the current limiter in the controller, so it should never get enough torque to skid.

The motor on the outside wheel will speed up, which will reduce the load on it. Under some conditions, the inside wheel may provide all the power, and the outside wheel would be essentially freewheeling. Unless there is motor braking, the outside wheel won't have any resistance to turning faster than the controller is telling it to.

Using two brushed motors in series will give a true differential action, but who wants brushed motors? This is not really what you want in snow or icy conditions either.

It should be possible to use wheel speed encoders to feedback to the controllers so they behave like ideal differentials. Software could be made to do this. This would be overkill, I think.

 

[Desertprep]

I am anxious for someone to try this - hopefully on a tadpole - and report back.

 

[Rassy]

I recently removed the motor on the front wheel of the Trike, and am now powering it by the two motors on the trailer, at 48V. They are brushed motors, but as far as the differential effect I don't think the brushed Vs Brushless matters. Anyway, on the non-steering wheels of my trailer this works great, and I believe on the rear wheels of a delta trike or a four-wheel electric vehicle the effect would be the same. However, it would be interesting to know what FredyFlatfoot's tadpole style trike would do with two front hub motors. I predict it would work slick. Has anyone tried two front hub motors on a tadpole's steered wheels?